Day of the week in Python

D = int(input("Enter day: "))

M = int(input("Enter month number: "))

Y = int(input("Enter year: "))

MCode = [0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5]

CCode = [6, 4, 2, 0, 6]      # 1600-1699, 1700-1799, etc.

Days = ["Sunday", "Monday", "Tuesday", "Wednesday",

        "Thursday", "Friday", "Saturday"]

C = (Y // 100) % 16          # C -> Century

num = D + MCode[M-1] + (Y%100) + ((Y%100)//4) + CCode[C]

print(Days[num%7])

Explanation below

Inputs				Output
Month Codes		Century Codes		Day Codes
January	0	1600 - 1699	6	Sunday	0
February	3	1700 - 1799	4	Monday	1
March	3	1800 - 1899	2	Tuesday	2
April	6	1900 - 1999	0	Wednesday	3
May	1	2000 - 2199	6	Thursday	4
June	4			Friday	5
July	6			Saturday	6
August	2
September	5
October	0
November	3
December	5

11 – 08 – 1966

(Day +MCode + Last 2 digits of year + Last 2 digits of year // 4 + CCode) % 7

(11   +      2      +             66                   +                66                // 4 +     0) % 7

(11   +      2      +             66                   +                           16             +     0) % 7

95 % 7 = 13 4/7

4 (Thursday)